1. Field of the Invention
The present invention relates to an image processing apparatus, particularly to an apparatus to transmit moving image data.
2. Description of the Related Art
In recent years, systems capable of dealing with audio data, image data, and other data have become widespread. Accordingly, the need for transmitting/receiving moving image data of various frame rates has been increasing. Under these circumstances, a data structure capable of changing a frame rate is specified in the MPEG (Moving Picture Expert Group) standard.
For example, in the MPEG-1 and MPEG-2 standards, a frame rate specified by a flag is selected from among encoded several frame rates (frame rate values). The MPEG-4 standard adopts a data structure in which display-time data is inserted into each frame of moving image data. With this data structure, both a fixed frame rate and a variable frame rate can be set in the MPEG-4.
Also, in recent years, there has been suggested a configuration of transmitting/receiving additional information, including a frame frequency and a horizontal synchronization frequency of image data to be output and a pixel size of an image, in a system including a computer and a display (e.g., see Japanese Patent Laid-Open No. 10-69251). Such additional information is transmitted/received in a DVI (digital visual interface) standard, for example. Thus, those parameters can be changed in the state where the power of an image data transmitting apparatus (e.g., computer) and an image data receiving apparatus (e.g., display apparatus) is turned on.
As described above, when moving image data encoded by the MPEG-1 or MPEG-2 standard is to be decoded, the frame rate can be detected only after the moving image data has been input to a decoder and a flag indicating the frame rate has been detected.
Also, when moving image data encoded by the MPEG-4 standard is to be decoded, change in frame rate can be detected only after a decoder has detected display-time information of each frame.
For this reason, in a display apparatus to display moving images corresponding to decoded moving image data, a displayed image is distorted or change of displayed images delays disadvantageously if the frame rate of the displayed moving image data changes.
In the DVI standard, it is necessary to reset or initialize an element in a transmitting/receiving apparatus, such as an image buffer, when a frame rate is changed. In this case, too, a displayed image disappears or blacks when the frame rate is changed.